GASTROENTEROLOGY
INTESTINAL ISCHEMIA
ACUTE MESENTERIC ISCHEMIA (25%)
Etiologies
• SMA embolism (50%): from LA (AF), LV (↓ EF) or valves; SMA most prone to embolism
• Nonocclusive mesenteric ischemia (25%): transient intestinal hypoperfusion due to ↓ CO, atherosclerosis, sepsis, drugs that ↓ gut perfusion (pressors, cocaine, dig, diuretics)
• SMA thrombosis (10%): usually at site of atherosclerosis, often at origin of artery
• Venous thrombosis (10%): hypercoagulable states, portal hypertension, IBD, malignancy, inflammation (pancreatitis, peritonitis), pregnancy, trauma, surgery
• Focal segmental ischemia of the small bowel (<5%): vascular occlusion to small segments of the small bowel (vasculitis, atheromatous emboli, strangulated hernias, XRT)
Clinical manifestations
• Occlusive: sudden abd pain out of proportion to abdominal tenderness on exam at leastinitially (2–4 h) until severe ischemia → frank infarction w/ peritoneal signs
• Nonocclusive: abd distention & pain, though up to 25% may be pain-free, 
N/V; often in setting of CHF ± h/o chronic mesenteric ischemia sx
• Hematochezia due to mucosal sloughing (right colon supplied by SMA)
• “Intestinal angina”: postprandial abd pain, early satiety, & ↓ wt from gastric vascular “steal”; may occur wks to mos before onset of acute pain in Pts w/ chronic mesenteric ischemia
Physical exam
• May be unremarkable, or may only show abdominal distention; FOBT ~75% of Pts
• Bowel infarction suggested by peritoneal signs (diffuse tenderness, rebound, guarding)
Diagnostic studies
• Dx relies on high level of suspicion; rapid dx essential to avoid infarction (occurs w/in h)
• Laboratory: often nl; ~75% ↑ WBC; ↑ amylase, LDH, phosphate, D-dimer; ~50% acidosis w/ ↑ lactate (late)
• KUB: nl early before infarct; “thumbprinting,” ileus, pneumatosis in later stages
• CT angiography (arterial phase imaging): noninvasive test of choice; can detect thrombi in mesenteric vessels, colonic dilatation, bowel wall thickening, pneumatosis/ portal venous gas; venous phase imaging for dx of mesenteric vein thrombosis
• Angiography: gold standard; potentially therapeutic; indicated if vasc occlusion suspected
Treatment
• Fluid resuscitation, optimize hemodynamics (minimize pressors); broad-spectrum abx
• Emergent surgery for prompt resection of necrotic bowel if evidence of peritonitis
• Anticoagulation for arterial & venous thrombosis and embolic disease
• Papaverine (vasodilator) catheter-directed infusion into SMA, typically in nonocclu- sive ischemia when spasm is considered the primary cause of the ischemia
• SMA embolism: consider fibrinolytic; if no quick improvement → surgical embolectomy if possible, o/w aortomesenteric bypass
• SMA thrombosis: percutaneous or surgical revascularization (J Vasc Surg 2009;50:341)
• Nonocclusive: correct underlying cause (esp. cardiac)
• Consider angioplasty/stent vs. surg revasc in cases of chronic mesenteric ischemia if: ≥2 vessels or occl SMA, supportive clinical hx, & other etiologies for abd pain excluded
Prognosis
• Mortality 20 to >70% if bowel infarcted; dx prior to infarction strongest predictor of survival
ISCHEMIC COLITIS (75%)
Definition & pathophysiology
• Nonocclusive disease 2° to Ds in systemic circulation or anatomic/fxnal Ds in local mesenteric vasculature; often underlying etiology unknown, frequently seen in elderly
• “Watershed” areas (splenic flexure & rectosigmoid) most susceptible, 25% involve R side
Clinical manifestations, diagnosis, & treatment
• Disease spectrum: reversible colopathy (35%), transient colitis (15%), chronic ulcerating colitis (20%), resulting stricture (10%), gangrene (15%), fulminant colitis (<5%)
• Usually p/w cramping LLQ pain w/ overtly bloody stool; fever and peritoneal signs should raise clinical suspicion for infarction
• Dx: r/o infectious colitis; consider flex sig/colonoscopy if sx persist and no alternative etiology identified (only if peritonitis not present, o/w avoid overdistention of colon)
• Treatment: bowel rest, IV fluids, broad-spectrum abx, serial abd exams; surgery for infarction, fulminant colitis, hemorrhage, failure of med Rx, recurrent sepsis, stricture
• Resolution w/in 48 h w/ conservative measures occurs in >50% of cases